Vulnerability of Ecological Condition to the Sequencing of Wet and Dry Spells Prior to and during the Murray-Darling Basin Millennium Drought

Abstract

Droughts are a significant stressor for water supply systems and freshwater ecosystems. Studies on drought risks and impacts have focused on the frequency, duration, and severity of droughts. While these metrics may be appropriate for understanding the risks to consumptive water supply because they directly relate to deficits in catchment yields, they are insufficient to represent risks to ecosystems whose conditions are highly dependent on the sequencing of particular flow events. This paper explores the importance of differing sequences of wet and dry spells preceding and within a recorded drought period to water management objectives. A number of hydrological scenarios were developed by systematically making modest adjustments to the input hydrological sequences on an annual basis. A case study of the Murray Region (Australia) shows that sequencing of wet and dry spells both preceding and within a drought can have substantial influences on ecological outcomes during the drought period. This has implications for developing scenarios for assessing climate change risks, highlighting the importance of both traditional drought indices and the natural variability of hydrological sequences.